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Modelling the influence of infrared preheating and temperature uniformity in forming of powder-impregnated thermoplastic composites

Abstract : Non-isothermal thermoforming of thermoplastic composites, in which a preconsolidated blank is heated above the melting temperature of the matrix before being formed in a press, is a process well adapted to the high production rates of automotive structural parts, allowing for cycle times < 1 min. Numerical tools to predict the apparition of manufacturing-induced defects based on the process parameters used are of an obvious industrial interest to avoid relying on a cost and time intensive trial-and-error approach. This thesis focused on the development of a comprehensive simulation of the forming of powder-impregnated PA66/glass composites, modelling explicitly the infrared preheating step to investigate the effect of temperature homogeneity on shape defects. The thermophysical and optical properties of the material were characterized experimentally at two levels of consolidation, and as a function of temperature when relevant. The structure of the non-consolidated material leads to a less uniform heating, compared to preconsolidated blanks. A finite element model based on the radiosity method to compute the radiative heat transfer was used to simulate the preheating step; this approach was validated against experimental results from a custom-built infrared oven. The model has been used to investigate the effect of blank sag on temperature distribution, and an optimization method to determine the oven parameters based on a desired temperature field has been presented. The mechanical behaviour of the woven composite during forming was modelled with a hypoelastic continuum approach, implemented in Abaqus/Explicit. The model parameters were determined from experimental tensile tests and in-plane shear tests at various temperatures and shear rates. Non-isothermal simulations of the forming of hemispherical parts were conducted, using the temperature field predicted from the preheating simulation as an input, and showed good agreement with that observed on parts formed on a lab-scale thermoforming setup.
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Théo Baumard. Modelling the influence of infrared preheating and temperature uniformity in forming of powder-impregnated thermoplastic composites. Materials. Ecole des Mines d'Albi-Carmaux; Queen's university (Belfast), 2019. English. ⟨NNT : 2019EMAC0010⟩. ⟨tel-02903087⟩

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